Five out of five NFL linebackers agree: It is difficult to push, pull, or drag Adrian Peterson to the ground, particularly when he is running and would prefer to keep running. At times the Vikings' second-year running back scarcely seems human, particularly when he breaches the defensive line and just explodes into the secondary, as if someone hit a fast-forward button that only applies to him. Coming off one of the most enthralling rookie seasons in NFL history, the 6' 1", 215-pounder entered last season amid ultra-high expectations, and he didn't disappoint. His 1,760 rushing yards led the NFL, and he made it to his second Pro Bowl in as many years. Okay, so his season wasn't flawless—he became fumble-prone midseason and coughed up the pigskin nine times by season's end—but 2008 saw Peterson mature from a dazzling but inexperienced rookie to a bona fide superstar. He has the potential to be one of the game's all-time greats. And there aren't that many second-year players, in any sport, of which you can say the same.